The present invention relates in general to techniques for obtaining improved images by compensation methods. In particular it relates to a method for compensating defective pixels in a Spatial Light Modulator (SLM), used in optical lithography. It also relates to an apparatus for patterning a work piece comprising such a method and a method for detecting defective pixels.
Lithographic production is useful for integrated circuits, masks, reticles, flat panel displays, micro-mechanical or micro-optical devices and packaging devices, e.g. lead frames and MCM""s. Lithographic production may involve an optical system to image a master pattern from a computer-controlled reticle onto a workpiece. A suitable workpiece may comprise a layer sensitive to electromagnetic radiation, for example visible or non-visible light. An example of such a system is described in WO 9945435 with the same inventor and applicant as the present invention.
Said computer controlled reticle may be a Spatial Light Modulator (SLM) comprising a one or two dimensional array or matrix of reflective movable micro mirrors, a one or two dimensional array or matrix of transmissive LCD crystals, or other similar programmable one- or two dimensional arrays based on gratings effects, interference effects or mechanical elements (e.g., shutters).
In general, these computer controlled reticles may be used for the formation of images in a variety of ways. These reticles, such as an SLM, include many modulating elements or pixels, in some instances million or more pixels. For example a problem with Spatial Light Modulators is that one or a plurality of pixels in a given SLM may be defective, i.e. they may not respond to a control signal as intended.
These defective pixels in a computer controlled reticle may limiting the resolution and accuracy available for their use in optical imaging; e.g., the production of printed patterns on a workpiece may be limited as to its line widths and accuracy.
Therefore, there is a need in the art for a method, which effectively and precisely finds and compensates for defective pixels in the SLM.
In view of the foregoing background, the compensation for defective pixels in the SLM, such as for example a mirror elements stuck in a specific position, is useful to form images having sub micron line widths with tolerances approaching 5 nm.
Accordingly, it is an object of the present invention to improve the images formed using spatial light modulators by providing an improved method for the compensation of defective pixels.
In a first embodiment, the invention provides a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting in a writing pass an image of said modulator on said work piece, and performing a compensation for defective pixels in at least one other writing pass.
In another embodiment of the invention said electromagnetic radiation is a pulsed laser source.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a single compensating pixel in another writing pass.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a plurality of compensating pixel in another writing pass.
In another embodiment of the invention said SLM is illuminated by a radiation dose in the different writing passes.
In another embodiment of the invention said SLM is illuminated by different radiation intensities in the different writing passes.
In another embodiment of the invention said SLM is a transmissive Spatial Light Modulator.
In another embodiment of the invention said SLM is a reflective Spatial Light Modulator.
In another embodiment of the invention the pixels in said SLM is operated in an analog manner.
The invention relates also to a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting an image of said SLM on the detector arrangement for measuring a dose of radiation, and performing a compensation of said defective pixel by at least one of the most adjacent pixels in the SLM.
In another embodiment of the invention said compensation is performed by assigning said at least one of the most adjacent pixels by a value given by subtraction of an intended pixel value by a actual pixel value divided by the number of most adjacent pixels used for compensation.
The invention relates also to a method for compensating the impact of at least one defective pixel in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered at least partially with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, setting the pixels in said SLM in a predetermined state, illuminating by a radiation source said SLM, projecting the image of the SLM onto the detector arrangement that measures dose of the SLM pixels, identifying defective pixels, and performing a compensation for said defective pixels in at least one writing pass.
The invention relates also to a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting in a first writing pass an image of said modulator on said work piece using a first set of pixels in said SLM, performing a pre compensation for defective pixels in at least one subsequent writing pass in at least one prior writing pass, and projecting in at least a second writing pass said image of said modulator on said work piece using at least a second set of pixels in said SLM.
In another embodiment of the invention, said method further comprising the action of, performing a post compensation for defective pixels in at least one prior writing step in at least one subsequent writing pass.
In another embodiment of the invention a post compensation for defective pixels in at least one prior writing step in at least one subsequent writing pass is performed instead of said pre compensation.
In another embodiment of the invention said electromagnetic radiation is a pulsed laser source.
In another embodiment of the invention, said method further comprising the action of, including at least one pixel in said first set of pixels in said at least second set of pixels.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a single compensating pixel in another writing pass.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a plurality of compensating pixels in another writing pass.
In another embodiment of the invention said SLM is illuminated by the same radiation dose in different writing passes.
In another embodiment of the invention said SLM is illuminated by different radiation dose in different writing passes.
In another embodiment of the invention said SLM is a transmissive Spatial Light Modulator.
In another embodiment of the invention said SLM is a reflective Spatial Light Modulator.
In another embodiment of the invention the pixels in said SLM is operated in an analog manner.
In another embodiment of the invention an image of said pixels in said first writing pass is displaced in said SLM relative said image of said pixels in said second writing pass by one or a plurality of pixels.
In another embodiment of the invention an image of said pixels in said first writing pass is displaced on said workpiece relative said image of said pixels in said second writing pass by at least a fraction of a pixel.
In another embodiment of the invention said first set of pixels belongs to a first SLM and said second set of pixels belong to a second SLM.
In another embodiment of the invention said first and second SLMs are illuminated simultaneously.
In another embodiment of the invention said first and second SLMs are illuminated by different radiation intensities.
The invention relates also to an apparatus for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation, comprising a source for emitting electromagnetic radiation, a projection system to project in a first writing pass an image of said modulator on said work piece using a first set of pixels in said SLM, means for performing a pre compensation of defective pixels in at least one subsequent writing pass in at least one prior writing pass, a projection system to project in at least a second writing pass said image of said modulator on said work piece using at least a second set of pixels in said SLM, means for performing a post compensation of defective pixels in at least one prior writing pass in at least one latter writing pass.
In another embodiment of the invention said electromagnetic radiation is a pulsed laser source.
In another embodiment of the invention at least one pixel in said first set of pixels is included in said at least a second set of pixels.
In another embodiment of the invention said projection system to project in at least a second writing pass comprises, said SLM reprogrammed with the image to be written on said work piece with said at least second set of pixels, a movable stage upon which stage said work piece is arranged in order to illuminate the same feature on said work piece with said at least second writing pass as said first writing pass.
In another embodiment of the invention said movable stage is moved the length of N SLM pixels.
In another embodiment of the invention said stage is moved along a row of pixels.
In another embodiment of the invention said movable stage is moved along a column of pixels.
In another embodiment of the invention said movable stage is moved along both a row of pixels and a column of pixels.
In another embodiment of the invention said movable stage is moved the length of N SLM pixels plus a fraction of a SLM pixel.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a single compensating pixel in another writing pass.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a plurality of compensating pixel in another writing pass.
In another embodiment of the invention said SLM is illuminated by a same radiation dose in the different writing passes.
In another embodiment of the invention said SLM is illuminated by different radiation intensities in the different writing passes.
In another embodiment of the invention said SLM is a transmissive Spatial Light Modulator.
In another embodiment of the invention said SLM is a reflective Spatial Light Modulator.
In another embodiment of the invention the pixels in said SLM is operated in an analog manner.
The invention relates also to an apparatus for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation, comprising a source for emitting electromagnetic radiation, a projection system for illuminating said SLM, having a plurality of modulating elements (pixels), by said radiation and projecting in a writing pass an image of said modulator on said work piece, the detector arrangement (65) for measuring the dose of pixels from the image of the SLM and a computer (66) for performing a compensation for defective pixels in at least one other writing pass out of said image on said detector (65).
The invention relates also to an apparatus for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) (30) when creating a pattern of the SLM (30) on a work piece (60) covered with a layer sensitive to electromagnetic radiation, comprising a source for emitting electromagnetic radiation, a projection system for illuminating said SLM (30), having a plurality of modulating elements (pixels), by said radiation and projecting in a writing pass an image of said modulator (30) on said work piece (60), the detector arrangement (65) for measuring the dose of pixels from the image of the SLM, and a computer (66) for performing a compensation for defective pixels (110) by using at least one of the most adjacent pixels (111, 112, 113, 114, 115, 116, 117, 118) to said defective pixel (110).
In another embodiment of the invention the pixel intensities are detected by said detector (65) whenever a new work piece (60) is to be patterned.
The invention also relates to a method for detecting at least one defective pixel in at least one SLM. Said method comprising the actions of addressing all pixels in said at least one SLM with a first steering signal, illuminating said at least one SLM with electromagnetic radiation, recording an image of said at least one SLM, computing a gradient field of the recorded image, computing a divergence of the gradient field, identifying extreme values from the computed divergence which corresponds to defective pixels.
In another embodiment said invention further comprising the actions of addressing all pixels said at least one SLM with a second steering signal, illuminating said at least one SLM with electromagnetic radiation, recording an image of said at least one SLM, computing a gradient field of the recorded image, computing a divergence of the gradient field, identifying extreme values from the computed divergence, where defective pixels corresponds to extreme values from said first steering signal and said second steering signal representing same pixels.
The invention also relates to a method for detecting at least one defective pixel in at least one SLM. Said method comprising the actions of addressing all pixels in said at least one SLM with a first steering signal, illuminating said at least one SLM with electromagnetic radiation, recording a first image of said at least one SLM, addressing all pixels in said at least one SLM with a second steering signal, illuminating said at least one SLM with electromagnetic radiation, recording a second image of said at least one SLM, computing the difference between said first image and said second image, identifying bad pixels where the computed difference has a local minimum.
The invention also relates to a method for detecting at least one defective pixel in at least one SLM Said method comprising the actions of addressing a pattern to said at least one SLM, illuminating said SLM with electromagnetic radiation, recording a first image of said at least one SLM, comparing said recorded image with pattern data at feature edges, identifying bad pixels where the feature edge is moved a predetermined distance.
In another embodiment said pattern is a chessboard pattern.
In another embodiment said pattern is a pattern with parallel lines.
In still another embodiment said method further comprising the action of addressing said pattern with another set of pixels in said at least one SLM, illuminating said SLM with electromagnetic radiation, recording a second image of said at least one SLM, comparing said recorded second image with pattern data at feature edges, identifying bad pixels where the feature edge is moved a predetermined distance.
In still another embodiment said method further comprising the action of comparing the feature edge movement in said first image with said second image for identifying bad pixels stuck at intermediate values.
In yet another embodiment said different writing passes is performed by means of one SLM.
In yet another embodiment said different areas of said SLM are used in the different writing passes.
In yet another embodiment said different writing passes is performed by means of a plurality of SLMs.
In yet another embodiment said different writing passes is performed by means of one SLM.
In yet another embodiment said different areas of said SLM are used in the different writing passes.
In yet another embodiment said different writing passes is performed by means of a plurality of SLMs.